1. FIELD OF THE INVENTION
The present invention relates to a recording/reproducing apparatus using a flexible magnetic disk and a recording/reproducing method using the magnetic disk, and more particularly to the tracking of a magnetic head unit.
2. DESCRIPTION OF THE RELATED ART
Heretofore, there has been proposed a magnetic disk having grooves formed in a magnetic layer for the purpose of tracking servocontrol, a recording/reproducing apparatus using such a magnetic disk, and so forth (see, by way of example, U.S. Pat. No. 4,958,245 and U.S. Pat. No. 4,961,123).
FIGS. 18 and 19 are enlarged sectional and plan views of a magnetic disk, respectively, for explaining the above type magnetic disk.
As shown in these drawings, a magnetic layer 101 is provided on the surface of a base film 100 formed of polyethylene telephthalate (PET), for instance, and grooves 102 for tracking servocontrol are formed by suitable means, e.g., laser machining, to extend in the direction of rotation of the magnetic disk. With that arrangement, the area between one groove 102 and the other groove 102 serves as a recording track 103 (see FIG. 19).
On the other hand, a recording/reproducing apparatus includes a light emitting element (not shown) for emitting a light beam 104 for tracking servocontrol to the surface of the magnetic disk, and light receiving elements 106a, 106b, 106c, 106d (see FIG. 19) for receiving reflected light 105 from the magnetic disk surface.
Thus, the light beam 104 emitted from the light emitting element is irradiated to the magnetic disk surface and the reflected light 105 therefrom is received by the light receiving elements 106a, 106b, 106c, 106d.
With the grooves 102 for tracking servocontrol formed in the magnetic layer 101 as mentioned above, the intensity of the light reflected by the recording track 103 is different from that of the light reflected by the groove 102. In the example shown in FIG. 19, since the light receiving elements 106b and 106d are arranged to receive respective beams of the reflected light from both of the grooves 102, tracking servocontrol for a magnetic head (not shown) is performed by comparing output values of the light receiving elements 106b and 106d and then making an adjustment so that both the output values become equal to each other.
Because of the conventional magnetic disk having the magnetic layer 101 thicker than 2.5 .mu.m, the reflected light 105 from the magnetic layer 101 can be received by the light receiving elements 106a, 106b, 106c, 106d with satisfactory results by integrating the light emitting element and the light receiving elements 106a, 106b, 106c, 106d into a unitary structure.
Meanwhile, in the art of the above type magnetic disk, the thickness of the magnetic layer has a tendency to become thinner for improved overwrite characteristics. Also, the base film being used is usually transparent. Accordingly, when a magnetic disk having a very thin magnetic layer is employed under tracking servocontrol, part or most of the light emitted toward the magnetic layer passes through both the magnetic layer and the base film. Therefore, the intensity of the reflected light becomes so weak that the tracking servocontrol cannot be performed in a proper manner, which leads to a problem in reliability. In view of the above, it would seem that the use of light receiving elements of the highest sensitivity would be able to detect even the reflected light of the weakest intensity, but this is not preferable due to the increasing cost involved.